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Module API_intro

The Blender Python API Reference

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This reference documents the Blender Python API, a growing collection of Python modules (libraries) that give access to part of the program's internal data and functions.

Through scripting Blender can be extended in real-time via Python, an impressive high level, multi-paradigm, open source language. Newcomers are recommended to start with the tutorial that comes with it.

This opens many interesting possibilities, ranging from automating repetitive tasks to adding new functionality to the program: procedural models, importers and exporters, even complex applications and so on. Blender itself comes with some scripts, but many others can be found in the Scripts & Plugins sections and forum posts at the Blender-related sites listed below.

Scripting and Blender:

These are the basic ways to execute scripts in Blender:
  1. They can be loaded or typed as text files in the Text Editor window, then executed with ALT+P.
  2. Via command line: blender -P <scriptname> will start Blender and execute the given script. <scriptname> can be a filename in the user's file system or the name of a text saved in a .blend Blender file: 'blender myfile.blend -P textname'.
  3. Via command line in background mode: use the '-b' flag (the order is important): blender -b <blendfile> -P <scriptname>. <blendfile> can be any .blend file, including the default .B.blend that is in Blender's home dir Blender.Get('homedir'). In this mode no window will be opened and the program will leave as soon as the script finishes execution.
  4. Properly registered scripts can be selected directly from the program's menus.
  5. Scriptlinks: these are also loaded or typed in the Text Editor window and can be linked to objects, materials or scenes using the Scriptlink buttons tab. Script links get executed automatically when their events (ONLOAD, REDRAW, FRAMECHANGED) are triggered. Normal scripts can create (Text) and link other scripts to objects and events, see Object.Object.addScriptLink, for example.
  6. A script can call another script (that will run in its own context, with its own global dictionary) with the Blender.Run module function.

Interaction with users:

Scripts can: You can read the documentation for the Window, Draw and BGL modules for more information and also check Python's site for external modules that might be useful to you. Note though that any imported module will become a requirement of your script, since Blender itself does not bundle external modules.

Command line mode:

Python was embedded in Blender, so to access bpython modules you need to run scripts from the program itself: you can't import the Blender module into an external Python interpreter.

On the other hand, for many tasks it's possible to control Blender via some automated process using scripts. Interested readers should learn about features like "OnLoad" script links, the "-b <blendfile>" (background mode) and "-P <script>" (run script) command line options and API calls like Blender.Save, Blender.Load, Blender.Quit and the Library and Render modules.

Note that command line scripts are run before Blender initializes its windows (and in '-b' mode no window will be initialized), so many functions that get or set window related attributes (like most in Window) don't work here. If you need those, use an ONLOAD script link (see Scene.Scene.addScriptLink) instead -- it's also possible to use a command line script to write or set an ONLOAD script link. Check the Blender.mode module var to know if Blender is being executed in "background" or "interactive" mode.

Click here for command line and background mode examples.

Demo mode:

Blender has a demo mode, where once started it can work without user intervention, "showing itself off". Demos can render stills and animations, play rendered or real-time animations, calculate radiosity simulations and do many other nifty things. If you want to turn a .blend file into a demo, write a script to run the show and link it as a scene "OnLoad" scriptlink. The demo will then be played automatically whenever this .blend file is opened, unless Blender was started with the "-y" parameter.

The Game Engine API:

Blender has a game engine for users to create and play 3d games. This engine lets programmers add scripts to improve game AI, control, etc, making more complex interaction and tricks possible. The game engine API is separate from the Blender Python API this document references and you can find its own ref doc in the docs section of the main sites below.

Blender Data Structures:

Programs manipulate data structures. Blender python scripts are no exception. Blender uses an Object Oriented architecture. The bpython interface tries to present Blender objects and their attributes in the same way you see them through the User Interface (the GUI). One key to bpython programming is understanding the information presented in Blender's OOPS window where Blender objects and their relationships are displayed.

Each Blender graphic element (Mesh, Lamp, Curve, etc.) is composed from two parts: an Object and ObData. The Object holds information about the position, rotation and size of the element. This is information that all elements have in common. The ObData holds information specific to that particular type of element.

Each Object has a link to its associated ObData. A single ObData may be shared by many Objects. A graphic element also has a link to a list of Materials. By default, this list is associated with the ObData.

All Blender objects have a unique name. However, the name is qualified by the type of the object. This means you can have a Lamp Object called Lamp.001 (OB:Lamp.001) and a Lamp ObData called Lamp.001 (LA:Lamp.001).

For a more in-depth look at Blender internals, and some understanding of why Blender works the way it does, see the Blender Architecture document.

A note to newbie script writers:

Interpreted languages are known to be much slower than compiled code, but for many applications the difference is negligible or acceptable. Also, with profiling (or even simple direct timing with Blender.sys.time) to identify slow areas and well thought optimizations, the speed can be considerably improved in many cases. Try some of the best bpython scripts to get an idea of what can be done, you may be surprised.

Version: 2.37

Author: The Blender Python Team


Requires: Blender 2.37 or newer.

See Also: main site, documentation and forum, user forum,, blender architecture: blender architecture document,,
Generated by Epydoc 2.1 on Mon Jun 13 15:31:22 2005